I'm leader of clan and I can't donate troops in the Clan War Castle. When I click the donate button, the game crashes and my mobile home page is displayed.
What causes this? Is there a way to fix it?
This is a known bug that was introduced in the th11 update. See the full list here. It is generally caused by having a barracks or dark barracks or dark spell factory upgrading. There is no fix for this yet, though once your upgrade completes, it seems to work again.